The present invention refers to apparatuses adapted for manufacturing metal articles, in particular of light alloy such as an aluminum alloy, by means of the known method of press—forging by cast in a die (squeeze die cast forging), also known as “liquid forging”, by which a molten metal is fed to one or more cavities of a die from a furnace arranged below the die, through a duct associated with the furnace, which metal undergoes a compression during the forging step.
The pressure applied to the metallic material during forging allows to oppose formation of micro-cracks in the forged articles, so that their structure turns out to be more compact and even, and characterized by a higher structural resistance with respect to that obtainable by previously known forging methods.
An apparatus of the type mentioned above, which is known by EP-A-1 472 027, comprises a die which may have a plurality of impressions which allow, for example, to manufacture at the same time a plurality of equal pieces or pieces different to each other during a single forging step. The upper portion of the die includes a series of movable punches, one for each impression of the die, which are rigidly connected to each other so as to undergo simultaneously a same movement with respect to the upper portion of the die, in order that they apply together a pressure on the metal constituting the articles to be forged.
Although this known apparatus turns out to be usually effective in the use, problems may arise when a plurality of articles have to be manufactured during a single forging step, in particular if the number of articles to be forged is high, or when a single article of big dimensions has to be manufactured by applying a pressure at a plurality of different zones thereof during the forging step. Mainly when aluminum based light alloys are used, small differences of temperature between different zones of the die at the impressions of the various articles, or of the single article of big dimensions, may involve differences in the surface tension of the molten metal fed into the impressions, and cause therefore a different dosing of the metal in the various impressions with a resulting different filling.
When the amount of molten metal fed to the various impressions does not correspond exactly to that expected, also the pressure applied to the various articles, or at different zones of a same article, during the forging step may be different from that expected, because of the fact that the various punches are connected to each other so as to move all together with of a same stroke, with the risk that in some forged articles, or at different zones of a same article, micro-cracks may originate, such as to weaken its structure and cause the need to reject them.